As shown in FIG. 1, a Universal Mobile Telecommunications System (UMTS) 100 includes a Universal Terrestrial Radio Access Network (UTRAN) in communication with User Equipment (UE). The UTRAN includes a Radio Network Controller (RNC). Further details regarding the UMTS can be ascertained from sections 5 and 6 of 3GPP TS 25.401 v4.0.0 (2001-03).
In the UMTS, the UE communicates with the UTRAN via cells to exchange of user information. In the UMTS, a cell is defined as a Radio Network object that can be uniquely identified by a UE from a cell ID that is broadcasted over a geographical area. In an effort to maintain continuous communication with the UTRAN, the UE monitors four sets of cells—the Active Set, Monitored Set, Detected Set and Virtual Active Set. The Active Set includes UTRAN cells with which the UE is in soft or softer handover with. Cells within the Active Set are active cells, while those not in the Active Set are non-active cells. User information is exchanged between the UE and UTRAN through the active cells. The Active Set contains only UTRAN cells and the cells are all under the same UMTS frequency.
The Monitored Set includes cells not currently in the Active Set that the UE is monitoring for handover according to a neighbor list assigned by the UTRAN. The Monitored Set may contain UTRAN and Global System for Mobile Communications (GSM) cells. The UTRAN cells may be under different UMTS frequencies. The Detected Set includes cells that are not in the Active Set or Monitored Set, but which are detected by the UE without RNC direction. In other words, the UE discovers these cells on its own, rather than according to a neighbor list assigned by the UTRAN. The UE reports only detected cells (UTRAN cells only) that are under the same frequency as the active cells (used frequency) and only when in a particular state. The Virtual Active Set is an Active Set associated with a non-used frequency. Cells in the Virtual Active Set are UTRAN cells that the UE is measuring for potential inter-frequency handover (hard handover). These cells are managed as a virtual active set using intra-frequency measurement criteria and events. After execution of the hard handover, the Virtual Active Set becomes the Active Set.
Each cell in the Active Set has a neighbor list of cells that includes cells that are likely candidates for handover. These cells are used to construct the Monitored Set. Currently, cells in the neighbor list are prioritized by the system operator when the list is provisioned. The priority may or may not be based on the likelihood of the cells being promoted to the Active Set. Thus, there is a need for a method of automatically ordering the neighbor list of a cell in the Active Set according to the likelihood that the cell will be promoted to the Active Set.